Motion artifact resulting from electrode and patient movement is a significant source of noise in making physiological recordings such as electrocardiograms (ECG), electroencephalograms (EEG), and electromyograms (EMG). This noise results in a contaminated signal being received from the electrode, and is particularly a problem in cases where it is necessary to make such recordings while the patient is engaged in activity. These artifacts arise from skin deformation which may be produced by forces transmitted through the skin-electrode interface or by forces on the skin generated by movement of the patient.
One approach taught in U.S. Pat. Nos. 4,503,860; 4,757,817; and 5,445,537 to limit such artifacts has been to provide means for anchoring a lead wire connecting the electrode to a recording device being used to make the recording. The anchor absorbs strains on the lead wire due to motion of the patient relative to the recording device and due to the weight and inertia of the lead wire as the patient moves, thus preventing these strains from being transmitted to the electrode itself. While such anchors minimize strains resulting from the lead wire, they do not address strains due to stretching and bending of the skin of the patient.
U.S. Pat. No. 5,355,883 teaches an electrode connector which incorporates a strain gauge. The strain gauge is accommodated in a protective cap of the connector, between a contact member which connects to the electrode and an interior region of the cap. The intent of the '883 device is to generate a strain signal from the strain gauge and subtract the strain signal from the contaminated signal received from the electrode to generate an uncontaminated signal. However, the '883 device only addresses strains experienced by the connector, and does not provide an index based upon the state of deformation of the skin where the electrode is positioned, which can effect the output signal from the electrode. Also, the '883 patent does not teach a method for processing the signals from the strain gauge to provide appropriate weighting of the strain signal with respect to the signal received from the electrode.
Thus, there is a need for a skin-mounted physiological recording electrode assembly which allows for measuring deformation of the skin to which the electrode assembly is mounted, and there is a need for a system which uses such electrode assemblies to remove motion artifacts from a contaminated signal received from the electrodes.